This invention relates to high power lasers for industrial applications and, more particularly, to collimating or focusing the beams from plurality of laser sources.
Because a diode laser source emits a beam which typically exhibits different degrees of divergence along different axes, a lens or series of lenses such as microlenses are typically used to help focus the emitted light. It should be understood that xe2x80x9cfocusingxe2x80x9d is used here in the sense which includes a range of effects that a lens may have on a diverging beam, from decreasing the divergence to collimation to convergence to a small spot. Generally, the emitting apertures of a laser diode are rectangular in shape with the long dimension having a size of typically hundreds of microns, while the short dimension is typically one micron in size. Diffraction effects cause the emerging radiation to diverge, with the divergence angle being inversely proportional to the size of the aperture. The short dimension of the aperture is comparable to the typical laser diode wavelength of approximately eight hundred nanometers; diffraction effects result in large beam divergence in this, the xe2x80x9cfast axisxe2x80x9d, direction which may be as high as seventy five degrees. The size of the divergence angle is known as the numerical aperture (NA), the beam having a lower numerical aperture along the direction of the stripe than perpendicular to the stripe. Typical values would be NA=0.1 and NA=0.33 respectively. In the applications of concern here, the radiation must be focused at some distance from the laser diode and it is desirable to concentrate the beam diameter so as to maximize the power density at the point of focus.
To provide more power than can be obtained from a single solid state laser, several laser sources can be assembled into a laser xe2x80x9cbarxe2x80x9d Koester U.S. Pat. No. 3,670,260; U.S. Pat. No. 4,185,891; and Sprague, et al U.S. Pat. No. 4,428,647, show various ways to compensate for the fact that laser bars emit spaced-apart beams. In particular, the ""891 and ""647 patents show the use of micro-lenses between the laser and an objective lens in which each micro-lens reduces the angle of divergence of a respective light beam leaving the emitting surface of the laser bar. Reducing the divergence angle of the beams allows the objective lens to reduce the beam spacing to a degree that is substantially less than the set spacing between the beams at the laser bar.
While the use of a microlens array reduces the divergence angle among the longitudinally separated beams emanating from the emitting sources of a diode laser, a laser bar which incorporates several, transversely separated diode lasers requires that an objective lens having a large numerical aperture be used if the beam is to be concentrated into a usefully small spot. Large numerical aperture objective lenses tend to be expensive. The problem becomes even more difficult when more power is required than can be delivered by a single laser bar. If it is attempted to use two laser bars, the lateral separation of their beams adds to the difficulty. It would be extremely advantageous to be able to focus such widely separated laser beams to an acceptable spot size without requiring the use of an expensive objective lens.
In accordance with the principles of the present invention, the laser beams from a pair of laterally separated stacks of laser diode bars are focused into a single vertical plane through the use of an array of interleaved, laterally reversed, identical, angular glass plates, each of said plates having a plurality of edge surfaces including a beam entrance edge surface, a beam exit edge surface and an alignment edge surface. Successive glass plates present complementary oblique entrance surfaces to the laser beams from the two stacks, each plate having an exit surface parallel to its entrance surface, the parallel entrance and exit surface of the plates being spaced apart to refract the laser beams so as to alternately overcome the lateral displacement of the beams from the stacks of laser bars.